travis: Add new job to build and test unix coverage in 32-bit mode.
travis: Add new job to build and test unix coverage in 32-bit mode.

selste/micropython,henriknelson/micropython,bvernoux/micropython,tobbad/micropython,henriknelson/micropython,pramasoul/micropython,selste/micropython,MrSurly/micropython,pozetroninc/micropython,selste/micropython,pozetroninc/micropython,tobbad/micropython,henriknelson/micropython,kerneltask/micropython,kerneltask/micropython,henriknelson/micropython,tobbad/micropython,henriknelson/micropython,MrSurly/micropython,adafruit/circuitpython,pozetroninc/micropython,pramasoul/micropython,MrSurly/micropython,selste/micropython,tobbad/micropython,pozetroninc/micropython,pramasoul/micropython,adafruit/circuitpython,bvernoux/micropython,MrSurly/micropython,kerneltask/micropython,tobbad/micropython,kerneltask/micropython,MrSurly/micropython,bvernoux/micropython,pramasoul/micropython,adafruit/circuitpython,adafruit/circuitpython,bvernoux/micropython,pramasoul/micropython,bvernoux/micropython,pozetroninc/micropython,adafruit/circuitpython,adafruit/circuitpython,kerneltask/micropython,selste/micropython